This invention relates to a frame structure for a vehicle.
The present application claims priority from Japanese Patent Application No. 2003-353946, the disclosure of which is incorporated herein by reference.
Conventionally, as shown in FIG. 4, rear side frames (hereinafter referred to as rear frames) 1 and 1′ disposed on both right and left sides of a vehicle body have been connected to each other through a cross member 2 which extends in a widthwise direction of the vehicle body below a rear floor, and have been configured to maintain a strength for supporting a bumper beam 5 fixed in a cantilever manner through a rear end panel 3 and through bumper stays 4 and 4′ and to maintain a rigidity of the vehicle body.
Incidentally, in this conventional frame structure, an impact load applied from a back side of the vehicle body to the bumper beam 5 due to a crash, for example, is transmitted through the bumper stays 4 and 4′ to the respective rear frames 1 and 1′ at a front side thereof. Accordingly, in order to avoid damages to the vehicle body in a low-speed rear crash at a speed of 8 km/h (about 5 mph), for instance, it is necessary to increase not only the strength of the bumper stays 4 and 4′ and the bumper beam 5 against the impact load from the back side, but also the rigidity (strength) of the rear frames 1 and 1′ in a longitudinal (front-to-back) direction for bearing a reactive force of the bumper beam 5.
In this case, increase in a thickness and a length of the respective members for the rigidity of the rear frames 1 and 1′ and the strength of the bumper stays 4 and 4′ against the impact load from the back side as well as the bumper beam 5 would result in further adding manufacturing costs and weight thereof.
Moreover, if the rigidity of the rear frames 1 and 1′ is increased in the longitudinal direction, the rear frame 1′ receiving an impact load in a rear offset crash at 80 km/h (about 50 mph) as shown in FIG. 4, for example, may be bent by a resistant force as indicated with the chain double-dashed line in FIG. 5 instead of an intentional axial crush.
When the rear frame 1′ receiving the impact load is bent without collapsing in an axial direction, an absorption of the impact load may not be achieved as designed, whereby an unintentional deformation of the rear floor above the rear frames 1 and 1′ may hurt passengers in the vehicle (see, for example, Japanese Patent Application Laid-Open No. Hei 11-101420).